1. (Industrial useful field)
This invention relates to a flywheel assembly which absorbs, for example, a torsional vibration of a drive-transmission system in an automobile.
2. (Prior art and its problem)
In FIG. 5 which is a schematic structural diagram of a convention clutch disc, 10 is an engine input side and 12 is an output side from which a power is transmitted to a transmission, for example. A first-state torsion spring 14a, a second-stage torsion spring 14b and a third-stage torsion spring 14c are interposed between the input side 10 and the output side 12. Specified torsion angle plays 14d and 14e are provided to the second-stage torsion spring 14b and the third-stage torsion spring 14c, respectively. Further, a first-stage hysteresis torque generating mechanism 16a, a second-stage hysteresis torque generating mechanism 16b and a third-stage hysteresis torque generating mechanism 16c are also interposed between input side 10 and output side 12. Plays 16d and 16e are provided to the second-stage hysteresis torque generating mechanism 16b and the third-state hysteresis torque generating mechanism 16c, respectively.
In the above-mentioned conventional embodiment, a torsion characteristic changes from a first-stage torsion characteristic Kd1 and a first-stage hysteresis characteristic Th1 which are both generated by the first-stage torsion spring 14a together with the first-stage hysteresis torque generating mechanism 16a, to a third-stage torsion characteristic Kd3 and a third-stage hysteresis characteristic Th3 which are both generated by the third-stage torsion spring 14c together with the third-stage hysteresis torque generating mechanism 16c, with an increase in a torsion angle as shown by FIG. 6 which is a graph representing a relation between a torsion angle 0 and a transmitted torque Tr. However, this characteristic has the following disadvantage.
Namely, it is desired to set the first-stage torsion characteristic Kd1 and third-stage torsion characteristic Kd3 to small values as a countermeasure against noises such as gear chattering generated from a transmission in its neutral position and gear chatterings generated from the transmission and a differential gear in their driving position. On the contrary, however, it is necessary to set the first-stage torsion characteristic Kd1 and third-stage torsion characteristic Kd3 to large values as a countermeasure against low frequency vibrations.
Consequently, the torsion characteristic of FIG. 6 is set up separately according to a characteristic required to each vehicle. Further, since a level of requirement for noise and vibration control of clutches has becomes increasingly higher in recent years, sometimes a characteristic which can never be dealt with by the conventional structure is required. Such a case is where conflicting countermeasures against noise and low frequency vibration are required simultaneously as mentioned above.
Therefore, technologies have been developed where vibrations from engine are positively absorbed even by the flywheel.
There has been prior arts, for example, where an auxiliary flywheel 26a and a damper 26b are interposed in series between a conventional clutch disc 20 and flywheel 22 and a crank shaft 24 as shown in FIG. 7 and the axillary flywheel 26a is installed in parallel with the flywheel 22 through a torsion spring 26c as shown in FIG. 8.
With regard to this kind of flywheel assembly, the applicant of the present invention has developed and applied for a patent a flywheel assembly, as shown in FIG. 9, which includes a first flywheel 104 fastened to an engine crank shaft 100 and engaged and disengaged by a clutch disc 102, A second flywheel 106 is installed concentrically with the first flywheel and set to a specified mass, A damper mechanism 108 is resiliently coupling to both flywheels A friction damping mechanism 112, which transmits an output from the second flywheel 106 to a spline hub 110 of the clutch disc 102, damps its vibration only when the clutch disc 102 contacts the first flywheel 104. (Japanese Patent Application No. 60-44298, co-pending U.S. patent application Ser. No. 836,365, now U.S. Pat. No. 4,751,993, dated June 21, 1988, West German Patent Application No. 36 07 398.9, French Patent Application No. 8603211).
On the other hand, an inertial damper set to a specified mass, for example, may be equipped to a propeller shaft in order to damp a torsional vibration of a so-called drive-transmission system from an enginer output shaft to a driven wheel of an automobile. The applicant of the present invention made this invention while intending to damp the torsional vibration of the drive-transmission system by the use of the flywheel assembly in place of the inertial damper.
Further, an inertial damper set to a specified mass, for example, may be connected to a propeller shaft in order to damp a torsional vibration of a so-called drive-transmission system from an engine output shaft to a driven wheel of automobile. In this case, however, when plural peaks of different vibration frequency are included in a vibration characteristic of the drive-transmission system, such damper can not exert its full damping performance adapted to the vibration frequencies of respective peaks.
Therefore, the applicant of the present invention has made this invention while intending to damp the torsional vibration of the drive-transmission system, which includes the plural peaks of different vibration in its vibration characteristic, by the use of the flywheel assembly in place of the inertial damper.